Horvath, Laszlo; Bilinski, Halka; Radics, Lajos; Ingri, Nils
Precipitation and characterization of two novel aluminum hydroxo phthalates formed in the presence of silicic acid.
Croatica Chemica Acta, 77
The present work, performed at constant ionic strength of 0.6 mol dm(-3) NaCl at 25 degreesC, is a continuation of long-term studies of the conditions necessary for initial clay formation in model systems containing organic acids, Al and Si. Solid phases and the precipitation boundary characterizing the system H+-Al3+-phthalic acid (H2L)-silicic acid were determined and compared with the previously found compound Al-2(OH)(4)L (-) 4H(2)O (A) of a monoclinic unit cell, which was formed in the absence of Si. Addition of Si induced precipitation of two novel compounds (B and C) of the orthorhombic unit cell. Compound B was formed at a low L/Al ratio (R less than or equal to 2) and was of variable composition: AlxSi1.450-0.725 (OH)(3.8+/-0.1x) L(.)6H(2)O. It was found by calculation that at R less than or equal to 2 the end member with x = 2, Al-2(OH)(4)L (.) 6H(2)O, determined the precipitation boundary. Compound C formed at R > 2 had the constant composition Al(OH)L (.) 3H(2)O. Formation constants beta(p,q,r) were determined for the general equation pH(+) + qAl(3+) + rL(2-) --> HpAlqLr. The obtained values for compounds B and C are: log beta(-4, 2, 1) = -7.40+/-0.10 and log beta (-1, 1, 1) = 1.55 +/- 0.05, respectively. In addition to chemical analysis, thermogravimetry (TG), X-ray diffraction (XRD), infrared spectroscopy (IR), solid state Al-27 MAS NMR, Si-29 MAS NMR and Na-23 MAS NMR techniques were used for better characterization of solids and to detect possible impurities in them. Aluminum was found to be hexa-coordinated in all compounds. The IR spectra suggest that the phthalate ion acted as a bidendate ligand, bridging two aluminum atoms in solids B and C.
||aluminum hydroxo phthalates; formation constants; effect of silicic acid; model clay formations; solid state NMR; Al-27 MAS NMR; Si-29 MAS NMR; Na-23 MAS NMR; 0.6 m Na(Cl); initial clay formation; aqueous-solution; hydrolyzed aluminum(iii); Na+ system; equilibrium; silicon(iv); complexes; 25-degrees-C; spectra
||NATURAL SCIENCES > Chemistry
||Division of Physical Chemistry
|Project title||Project leader||Project code||Project type|
|Multidisciplinarna sedimentološka istraživanja||Halka Bilinski||0098041||MZOS|
||12 Nov 2013 10:02
||27 Feb 2014 11:12
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